Micro-hydro systems

If you have access to the right stream or waterway, micro-hydro can be a reliable and economic way to generate your own electricity. Many small hydro schemes already exist on rivers and streams around New Zealand, and there are more opportunities to use water driven generation for remote farms and homes.

Types of micro-hydro facilities

Small scale hydroelectric facilities are generally classified into three sizes:

micro-hydro - up to 5 kW

mini-hydro - between 5 kW and 20 kW

small commercial hydro - between 20 kW and 10 MW.

Micro-hydro systems for houses and buildings are less than 5 kW, and in many cases less than 1 kW. Micro-hydro systems are best suited to rural areas on streams or waterways that flow all year round. The more vertical distance (head) you have between the point where you take the water and where the turbine is located, the more electricity you can generate.

How hydroelectricity works

Hydroelectricity systems use the force of running water to turn turbine blades, which spin a shaft connected to a generator. On rural sites they can be set up wherever water falls from a higher lever to a lower level, for example a waterfall, hillside, stream, or where a reservoir discharges into a river.

The type of turbine you need depends on the vertical distance the water falls and the rate the water flows. Pelton wheels are the type of turbine most commonly used for small scale domestic generation.

Small scale hydro systems don't usually need water storage. A portion of the stream or river is temporarily diverted through a pipe system to the micro-hydro turbine and generator. It's then returned to the same stream or river. This type of system has far less impact on the environment than large scale hydro schemes. If your small scale hydro scheme does need a dam or other form of water storage, you’ll need to get consent.

Does it make financial sense?

If you are looking at micro-hydro for purely economic reasons, then EECA strongly advises you do your sums carefully before you buy – especially if you are already connected to the electricity grid.

Costs vary depending on your location and requirements. Each micro-hydro system is designed to suit the specific features of a property. For a domestic system with a basic layout, expect to pay at least $10,000 to $15,000. Despite the high initial set up cost, running costs are low.

Factors influencing cost

Size - larger systems are generally cheaper per kW.

Geography and geology - depending on your site, it might take a few days or weeks to install your system.

Damming - if you need to build a dam to store water it will cost more.

Earth works and flood protection.

Length of water pipes and electrical cables.

Building and resource consents.

As the generating capacity of micro-hydro systems is quite small, you will most likely need to remain connected to the electricity grid and electricity continues to be purchased from a retailer during times when the micro-hydro system does not generate enough electricity.

Some households choose to go ‘off-grid’, disconnecting from the grid entirely and purchasing batteries to provide electricity when the micro-hydro system is not generating enough electricity to meet demand. Although battery prices are falling, this approach won’t make economic sense for most households that are already grid-connected. However, for new remote homes or farms facing a high cost to connect to the grid, going ‘off-grid’ with micro-hydro and batteries may be cost-effective.

Excess micro-hydro electricity can be sold to a retailer

At times, micro-hydro will generate more electricity than can be used, allowing grid-connected households to sell electricity to an electricity retailer. The retailer buys this electricity at a ‘buy-back rate’- these vary but are lower than the amount companies charge you for electricity. This means households with micro-hydro get greater value out of using the electricity they generate themselves, rather than selling it back to a retailer.

When considering micro-hydro, consider the buy-back rates on offer. You may need to switch from your current retailer to access a buy-back rate. The retailer offering the best buy-back rate may not necessarily charge the lowest for the electricity they sell.

Make sure the waterway is suitable - ideally it will have a good flow of water year round, and enough vertical drop over a small horizontal distance.

Ensure the water supply is reliable - compared with wind or solar generation, micro- hydro systems provide a constant flow of electricity (as long as the volume of water flowing remains constant).

Check out your rights to the water - you may need a resource consent from your regional council before using water to generate electricity.

You need prior approval to connect micro-hydro to the electricity grid, so contact your lines company before you start and talk to your electricity retailer also. A micro-hydro installation expert will be able to assist with this.

Although you may undertake some of the work to install micro-hydro yourself, all electrical work needs to comply with and be certified to NZ electrical standards. Your micro-hydro installation must comply with any local council regulations, so check with your council before going ahead.

Make allowances for maintenance - of mechanical, electrical and hydraulic equipment. This may only involve a few hours a month. Intake screens need to be kept clear of silt and debris, and collection lakes may require de-silting every few years.